When I picked this position for Pea and Martin I actually wanted to mix 3 different things.
Pea sleeps in fetal position, it's the typical position of those who are tough on the outside and sweet on the inside and don't easily trust others but when they open up they do it for real. Apparently it's a most typical position for women (who adopt it more than men).
The position I chose for Martin is the log. It's the typical position of those who are easy going, very sociable, very trusting and easily gullible.
To be sleeping as a log his leg would be straight.
The problem with Martin is... there are no beds big enough for him, being the poor guy 190 cm (6'2" almost 6'3") so he either has to let his feet stick out of the bed or he has to curl up a bit.
I guess, back home, he has had a bed custom built for him, ha ha ha.
The third thing I wanted to add is the fact that Pea is actually a hugger.
So remember when she was commenting to the doc about Kes - that she gets a hold of things and never let go? (but then we saw that Kes is actually the one sleeping within somebody's arms?).
My guess is... Pea has been waking up for years intertwined with her sister in the morning... thinking: oh my, she sure is a hugging freak.
When, in fact, poor Kes, had been squeezed the whole night by miss hugging freak herself ha ha ha.
It's such a small detail, sorry, not really evident enough to talk about it, not really worth telling a story about, probably... and not relevant to the storytelling itself - but my sister is like that too and that's what inspired me to hint at this little fact. She always tells people they take the whole space in bed, they snore and talk... but she is the one doing so and I swore I would tape her in her sleep one night, like that movie Paranormal, and then show it to her. Revenge!!!!